The ability to conveniently sense ionizing radiation is critical for a variety of applications including in medicine, defense, industrial food packaging, and pasteurization and sterilization techniques. Practical ranges for absorbed dose detection vary from the range of 1 Gy and below for human exposure, to upwards of hundreds of kGy for sterilization and decontamination procedures. See, e.g., K. M. Morehouse, V. Komolprasert, in Irradiat. Food Packag., American Chemical Society, 2004, pp. 1-11. Colorimetric sensors are convenient and can offer both simple and accurate read-out. Many such detection techniques, however, rely on a change in optical density triggered by irradiation of a photo-sensitive chromophore and require external equipment for read-out in addition to stringent storage conditions to avoid device failure. See, e.g., G. Shani, Radiation Dosimetry: Instrumentation and Methods, CRC Press LLC, Boca Raton, Fla., 2001. Some solution-based sensors which show clear colorimetric changes spanning a broader range of the visible spectrum provide an attractive means towards convenient, stand-alone sensors, but utilize inconvenient and toxic organic solvents. See, e.g., T. Schimitberger, G. R. Ferreira, M. F. Saraiva, A. G. C. Bianchi, R. F. Bianchi, Sensors Actuators B Chem. 2012, 168, 131; Z. Liu, W. Xue, Z. Cai, G. Zhang, D. Zhang, J. Mater. Chem. 2011, 21, 14487; T. Schimitberger, G. R. Ferreira, L. C. Akcelrud, M. F. Saraiva, R. F. Bianchi, Med. Eng. Phys. 2013, 35, 140. Among the many existing approaches, film-based sensing techniques are appealing for general use because they avoid potentially toxic solvents, however may also require sealed containment or have time-sensitive restrictions on read-out due to a lack of chemical stability post-irradiation. See, e.g., H. H. Mai, N. D. Duong, T. Kojima, Radiat. Phys. Chem. 2004, 69, 439; H. H. Mai, H. M. Solomon, M. Taguchi, T. Kojima, Radiat. Phys. Chem. 2008, 77, 457; J. M. G. Laranjeira, H. J. Khoury, W. M. de Azevedo, E. A. de Vasconcelos, E. F. da Silva Jr., Phys. E 2003, 17, 666; Y. S. Soliman, A. A. Basfar, R. I. Msalam, Radiat. Meas. 2014, 62, 45.
One-dimensional photonic crystals are periodic multilayer structures that rely on the interference of light to reflect a characteristic wavelength defined by the refractive index and thickness of each layer. See, e.g., E. Born, M. Wolf, Principles of Optics, Cambridge University Press, Cambridge, United Kingdom, 2002. One-dimensional photonic sensors have been explored extensively for detection of a wide range of analytes, including pH, ionic strength, temperature and a variety of small molecules. See, e.g., J. Ge, Y. Yin, Angew. Chem. 2011, 50, 1492; R. V. Nair, R. Vijaya, Prog. Quantum Electron. 2010, 34, 89. For example, Hayward et al. (M. C. Chiappelli, R. C. Hayward, Adv. Mater. 2012, 24, 6100) developed an approach to photonic multilayers for colorimetric temperature sensing based on photo-crosslinkable polymers.
Accordingly, there remains a need for the development of low-cost and chemically stable colorimetric sensors based on crosslinked polymer multilayers for radiation sensing. The use of crosslinked polymer layers or films as a platform for radiation sensing would allow for straightforward colorimetric read-out due to the reliance on changes in structural color, rather than absorption or emission of light by a chromophore.